1. Field of the Invention
The invention generally relates to an apparatus and method of monitoring radio frequency signals generated by piezoelectric effects, electrostrictive effects, or tribo-charging. More specifically, the invention relates to an apparatus and method of online monitoring for defective components within a combustion turbine.
2. Description of the Related Art
Combustion turbines typically operate at extremely high temperatures, for example, 2500xc2x0 F. to 2900xc2x0 F. (1371xc2x0 C. to 1593xc2x0 C). Such high temperatures can cause failure of various components unless they are protected from the heat. These components include the rotating blades of the turbine, and the vanes for directing gas flow within the turbine. A typical combustion turbine will have three to four rows each of blades and vanes, with approximately 50 to 100 blades or vanes per row, and will typically have approximately 500 total blades and vanes to protect. A commonly used material for vanes and blades is nickel-cobalt. These components are generally insulated by a thermal barrier coating so that the turbine can be operated at such high temperatures without causing excessive deterioration of these components. A typical thermal barrier coating is yttria-zirconia.
Currently, it is necessary to periodically stop the turbine and inspect the components for deterioration of the thermal barrier coating, defects in other coatings, or other defects, for example, formation of cracks in the underlying components. It would be desirable to monitor the condition of these components while the turbine is in use. Avoiding the need to periodically stop the turbine for inspection reduces downtime, increasing the turbine""s efficiency. Likewise, early detection of defects reduces repair costs and outage time, again increasing turbine efficiency. Although other systems of monitoring the condition of turbines during use have been proposed, the present invention provides the unique advantage of providing early detection of defects, and a means of locating the defect; simplifying the inspection and repair procedure once a defect is identified.
One proposed monitoring system is described in U.S. Pat. No. 5,552,711 issued to T. Deegan et al. on Sep. 3, 1996. This patent describes the monitoring of the condition of a structured surface by mounting microstrip antennas on the surface. The antennas comprise a dielectric substrate having a metallic patch on one side and completely plated by a conductor on the other side. The antennas may be integrated onto dielectric-piezoelectric substrates. The antennas receive power through electromagnetic radiation, possibly radio frequency waves. This power can be used to actuate the piezoelectric material. Signals from the piezoelectric material can be communicated through the microstrip antennas, thereby providing feedback regarding the condition of the surface. Uses for such a monitoring system include the monitoring of turbine blades. This system, however, requires the antennas to rotate with the turbine blades, thereby subjecting the antennas to additional stress.
Another proposed system for monitoring the condition of turbine blades is described in U.S. Pat. No. 5,970,393 issued to K. Khorrami et al. on Oct. 19, 1999. This system relies on the measurement of electromagnetic emissions of ions emitted by portions of the blade which are deteriorating. This system does not include a means for locating the stage wherein the failed component is located.
Accordingly, there is a need to provide an online monitor for the condition of combustion turbine components wherein the components of the monitor are supported by stationary portions of the turbine. Additionally, there is a need to identify the stage wherein a defect in the vanes and blades of a combustion turbine is forming. Further, there is a need to identify the location of the defective component, thereby simplifying and speeding the repair process.
The preferred embodiment of the invention is a method and apparatus for monitoring the condition of a component within a combustion turbine during operation of the turbine, such as the thermal barrier coating on the vanes and blades within the turbine. The principal embodiment of the system relies on detecting changes in the levels of the radio frequency signals generated by a piezoelectric effect or electrostrictive effect created between the coating and the substrate by gas pressure exerted on the vanes and blades, or from tribo-charging due to friction between the gas and the coating.
As the combustion turbine is operated, gas pressure flowing past the vanes and pushing against the blades will apply pressure to these components, causing an electric current resulting from a piezoelectric effect between the thermal barrier coating and the component. Although most materials producing a piezoelectric effect have been previously polarized by heating the material to a high temperature and passing DC current through the material, the present inventors have found that thermal barrier coatings exhibit a piezoelectric effect due to the polarity of molecular impurities within the coating. This current will cause the blade or vane to radiate a radio frequency signal. The piezoelectric effect, and consequently the magnitude of the radio signals, will vary according to the level of gas pressure, the coating properties, the bonding of the coating to the component, and the component material""s condition. Such variations in radio frequency signals may be detected using high-temperature micro-receiving antennas.
Alternatively, gas pressure on the blades will cause the blades to deflect under strain. This will cause an electric current between the thermal barrier coating and the component resulting from an electrostrictive effect. This current will cause the blade or vane to radiate a radio frequency signal. The electrostrictive effect, and consequently the magnitude of the radio signals, will vary according to the level of gas pressure, the coating properties, the bonding of the coating to the component, and the component material""s condition. As above, such variations in radio frequency signals may be detected using high-temperature micro-receiving antennas.
As a second alternative, friction between the gas and thermal barrier coating will result in tribo-charging. The result will be static electricity within the coating. This static electricity will cause the blade or vane to radiate a radio frequency signal. The tribo-charging, and consequently the magnitude of the radio signals, will vary according to the level of gas pressure, the coating properties, the bonding of the coating to the component, and the component material""s condition. As above, such variations in radio frequency signals may be detected using high-temperature micro-receiving antennas.
Regardless of the specific origin of the electricity created within the coating, the resulting radio frequency signal will encompass a wide range of frequencies. The signals received through the antenna may pass through a filter for filtering out frequency ranges present from other sources at that location, and an amplifier, before proceeding to a storage scope for viewing, and/or a computer for storage and analysis. Determining which blade requires servicing uses a single antenna proximate to one vane, in conjunction with a xe2x80x9cmarking bladexe2x80x9d designed to create a different radio frequency signal than the other blades as it passes the antenna. Such a marking blade may be produced by designing a coating intended to produce a greater piezoelectric effect, for example, by adding piezoelectric materials such as lead zircanate titanate to the coating. A blade requiring service will generate a different magnitude radio frequency signal than the remaining blades. When viewing a sequence of radio frequency signals, the number of signals between the marking blade and the blade generating a different magnitude signal can be used to determine the blade requiring service.
If monitoring of the coating on the vanes is also desired, an antenna corresponding to each vane may be used. A blade passing a vane will cause increased gas pressure on both the blade and the vane, resulting in each having a piezoelectric effect and each therefore giving off a radio frequency signal. The piezoelectric effect and resulting radio frequency signal within each vane is likely to be different from that within a blade, and can therefore be distinguished from the blade""s signal. Alternatively, a longer antenna extending adjacent to all vanes in a given row may be used.
It is therefore an aspect of the present invention to provide an apparatus for monitoring the condition of a thermal barrier coating within a combustion turbine while that turbine is operating.
It is another aspect of the present invention to provide a method of monitoring the condition of a thermal barrier coating within a combustion turbine while that turbine is operating.
It is a further aspect of the present invention to create electricity within the thermal barrier coating through a piezoelectric effect, electrostrictive effect, or tribo-charging.
It is another aspect of the present invention to create a radio frequency signal through electricity within the thermal barrier coating, with variations in the characteristics of the radio frequency signal varying according to the condition of the coating.
It is a further aspect of the present invention to provide a high temperature radio frequency antenna for receiving radio frequency signals generated within the thermal barrier coating.
It is another object of the present invention to provide a marking blade producing a different radio frequency signal than the other blades within a combustion turbine.
It is a further object of the present invention to analyze radio frequency signals received from the thermal barrier coating of the various vanes and blades, searching for a signal having a different magnitude or frequency than the remaining signals, indicating a blade or vane requiring service.
A better understanding of the present invention can be obtained from the following description, with reference to the drawings.